1. Field of the Invention
The invention relates to control of a four-wheel drive (4WD) vehicle, and particularly relates to control of a 4WD vehicle including a disconnect mechanism that interrupts power transmission (T/M) to a specific rotary element.
2. Description of Related Art
A 4WD vehicle is available which includes an auxiliary drive wheel to which power is transmitted from an engine (E/G) during a 4WD running, and a disconnect mechanism that is provided in a power T/M path between the E/G and the auxiliary drive wheel and interrupts power T/M to a specific rotary element for transmitting the power to the auxiliary drive wheel to thereby stop the rotation of the specific rotary element. 4WD vehicles described in Japanese Patent Application Publication No. 2010-100280 (JP 2010-100280 A) and Japanese Patent Application Publication No. 60-30433 (JP 60-30433 A) are examples thereof.
In the 4WD vehicle of each of JP 2010-100280 A and JP 60-30433 A, when a specific condition is satisfied, by operating the disconnect mechanism, co-rotation of the specific rotary element is prevented and fuel efficiency is thereby improved.
Incidentally, when the operation of the disconnect mechanism is canceled during a two-wheel drive (2WD) running that involves the operation of the disconnect mechanism, specifically, when the 2WD running is switched to a 4WD running or a normal 2WD running, the interruption of the power T/M to the specific rotary element of which the co-rotation has been prevented is canceled, and hence rotational inertia caused by an increase in the speed of the specific rotary element is increased. In JP 60-30433 A, by increasing an E/G torque when the running is switched from the 2WD running involving the operation of the disconnect mechanism to the 4WD running (cancellation of the operation of the disconnect mechanism), the increase in the rotational inertia of the specific rotary element is canceled, and a switching shock and an unnatural feeling of deceleration occurring during the switching are suppressed.